An important goal for researchers and pharmaceutical companies is to identify ways to use proteinaceous delivery vehicles to introduce novel molecules into the cytosol of cells, particularly into mammalian cells. While there are a number of methods for the delivery of bioactive peptides and proteins into mammalian cells for therapeutic and biotechnological purposes, there is still a specific need for methods to deliver larger molecules such as peptides, peptoids, proteins and small molecules that cannot traverse the plasma membrane by a simple diffusive process. Particularly, there is a need to deliver agents that are non-naturally occurring such modified peptides, D-peptides and other organic molecules not normally trafficked into a cell or manufactured by a cell.
The current technologies used to gain therapeutic access to the cytosol are limited in that they require large quantities of sample, have limited selectivity, and tend to not escape the endosome. The so called undruggable cytosolic fraction constitutes 80% of future therapeutic targets. Efficient delivery of the novel therapeutics is the main hurdle in drug development.